This post will be more about the stylistic choices made by these bands, rather than focusing on the qualities of the albums themselves.
Each new Mogwai album over the past ten years makes a solid first impression. But they never seem to grow on me -- each listen brings diminishing returns, and seldom reveal any new, unexpected levels of detail. A couple of tracks might stand out, but the rest fades into the background, not to be revisited once the next album cycle begins.
I searched my archives and had another look at what I wrote about "The Hawk Is Howling" nine (!!) years ago. Nothing has changed! Their albums still fill a "halfway gray area between loud and soft, between epic and succinct, between melodic and freeform". The ideas and clever melodies are there, but the payoffs aren't. Mogwai used to be all about building to the climax.
Creatively, I can't think of another formerly great band that's more in need of a complete reset. I keep coming back to "Rock Action", where every track seemed to announce it's own new microgenre, particularly the guitar noise/industrial slam opening track "Sine Wave". "Zidane -- A 21st Century Portrait" wasn't a classic but it took their music in a more blissed out direction that they had not fully explored to that point, and applied it to soundtracking the high drama of sport. That fresh approach is what drew me to the album.
In contrast, The National's latest album is a grower. At first I was disappointed at the lack of a standout powerhouse rock track such as "Graceless" from "Trouble Will Find Me". It's a quieter, more intimate album than its predecessor, with enough soft electronic embellishments to avoid repeating their earlier work, but not nearly enough to signify any kind of stylistic change. Previously, they would serve up maudlin with a wink and a style, treading that fine line between sad and humorous in a drunken pub rock package in a way that few bands other than Tindersticks have ever been able to master. Here, there's something more didactic about the lyrics, although I might soften that stance after additional listens. But "The System Only Dreams in Total Darkness" (what a title!) and "Day I Die" are tremendous singles, and the tension and urgency that the music needs is maintained from start to finish. There's a real buzz about an indie rock album made by forty somethings about relationship problems , which is weird and cool and confusing all at the same time.